Bio 206 Mini Exam 2 (plant circulation)

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Passive transport

• Energetically downhill 

• Spontaneous process (thermodynamically favorable) 

  • simple or facilitated diffusion (transmembrane channel protein that's specific to ion or molecule)

Active Transport

• Energetically “uphill”, against gradient

• Requires metabolic energy (often ATP hydrolysis) 

  • Sodium-potassium pump, changes conformation, accepting and releasing 

Plants use what to move water. minerals and sugars through specialized tubes?

pressure gradient and pressure potentials

• xylem (water and inorganic nutrients) and phloem (sugars like sucrose, can store complex comps.)

Features evolved to increase surface area for gas exchange

• spongy mesophyll (photosynthetic parenchyma, higher SA:V ratio, CO2 let in by stomata), roots, gills (water must be brought to them), alveoli (in animal lungs)

Secondary active transport

• Two substances move (one uphill, one down) 

  • Symporter (same direction across cell membrane) 

  • Antiporter (opposite directions) 

Fick’s law of diffusion for gases

• Rate of diffusion = k x A x ((p2 - p1)/D)

  • K = diffusion constant, depends on solubility of gas and temperature 

  • A = surface area for gas exchange 

  • P = difference in partial pressures of gas on either side of gas-exchange surface

  • D = distance (thickness of gas-exchange surface) 

ATP driven proton pump three gradients

pH, concentration, and electrical gradients

Solution

homogeneous, liquid mixture containing several substances

Water potential

1. potential energy, the ability for water to do work, measure of free energy (megaPascals, Mpa)

2. Ψ = Ψ_s + Ψ_P

3. Water wants to go to areas of low water potential, where is does less work

Solutes

dissolved substances, minor component

Solute potential

Tendency for water to move in response to differences in solute concentration, always negative cus measured relative to the solute potential of pure water 

• Solute binds water molecules, removing free water.

• Higher solute concentration = lower solute potential

hypertonic

more solutes, less water

hypotonic

less solutes, more water

Isotonic

equal amounts of solute on both sides of the membrane

Turgor pressure

pressure that is exerted by the fluid (eg water) against the cell wall

Water Potential In Soil?

1. In dry soils, water can’t flow freely and adheres to the soil, lowering water potential

2. In salt soils, the water binds to solutes, reducing water potential

Water-potential gradient

Water will always flow from high potential to low potential

• water flows from high potential at roots to low potential atmosphere in the leaves

Symplastic route

water goes inside the plasma membrane, passes through symplast via plasmodesmata

Transmembrane route

water moves across membrane, often through aquaporin

Apoplastic route

outside plasma membranes, through apoplast 

Casparian Strip

a narrow band of wax secreted by tightly packed Endodermal cells 

1. Blocks apoplastic route, forces water cross at least two cellmembrane (regulates toxins)

2. Suberin: a waterproof barrier where endodermal cells contact each other.

Surface tension

minimize total surface area of air-water interface because of hydrogen bonds

Cohesion

holds water molecules in the water column together, molecular attraction among like molecules

Adhesion

1. molecular attraction among dissimilar molecules 

2. water attracted to glass is pulled up against the force of gravity

Translocation

movement of sugars by bulk flow in multiple direction through plant

Xylem

• has traecheids and vessel elements (angiosperm only) 

  • Moving water and minerals 

Phloem

• has sieve plates and companion cells 

Move photosynthate (a sugar or other substance made by photosynthesis)

Cohesion-tension theory

• Transpiration is the main driver of water movement in the xylem. It creates negative pressure (tension) at the leaf surface, drawing water from the leaf through the stomata.

• Water from the roots is pulled up by the tension. Negative water potential draws water from the soil into the root hairs, then into the root xylem

• Cohesion and adhesion draw water up the xylem.

Stomata

Waxy cuticle on leave can’t exchange gases like CO2, so there us a pore.

• guard cells control opening and closing of stomata

• Trichome (epidermis hairs) inside stomata reduce the chance of losing water 

• open when:

  • Blue light is sensed by protein or pigment which initiates photo receptors, which starts a proton pump moving H out of the cell, creates electrical gradient and solutes enter the cell

  • As solute concentration increases, solute potential decreases inside, water moves inside